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Vol. 8. Issue 6.
Pages 6106-6114 (November - December 2019)
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Vol. 8. Issue 6.
Pages 6106-6114 (November - December 2019)
Original Article
DOI: 10.1016/j.jmrt.2019.10.005
Open Access
A Case Study On Concrete Column Strength Improvement with Different steel fibers and polypropylene fibers
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Rafid Saeed Atea
Jabir Ibn Hayyan Medical University, Najaf, Iraq
Article information
Abstract
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Tables (7)
Table 1. Chemical composition for silica fume.*
Table 2. Physical requirements and pozzolanic activity index for condensed silica fume(SF).*
Table 3. Properties of the used polypropylene fibers.*
Table 4. properties of steel bars.*
Table 5. Details of the column specimens.
Table 6. Results of mechanical properties of hardened tests.
Table 7. Maximum strength capacity fPmax for tested column specimens.
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Abstract

High presentation concrete is chiefly cast-off in multistory constructions where it expressively lessening the measurements of columns, which styles it a more economical excellent for building than normal strength concrete. In seismic area, high enactment concrete posses more complications, since it has less ductility in comparison with normal concrete. The purpose of this research is to detect the combined consequence of fibers and ties on the conduct of reinforced columns and to advance their ductility. This study presents an investigational valuation of strength and ductility of ordinary and high presentation concrete short columns limited by tie with and without steel fibers and polypropylene fibers. Five square concrete columns (100×100×1000) mm were established. The variables considered were, concrete strength, volume percentage of longitudinal reinforcement (4.52%), volumetric ratio of lateral reinforcement (spacing between ties) (5.58%) volume fraction of fibers (0.5% and 0.75%), form of fibers (hooked steel fiber and polypropylene) and phase ratio of steel fibers (100) (length 50mm and diameter 0.5mm) and (60) (length 30mm and diameter 0.5mm). The column specimens were tested under axial load. The values presented that the adding of steel fibers (volume friction 0.75% and aspect ratio 100) for high presentation concrete improves the compressive strength, splitting tensile strength, flexural strength, and static modulus of elasticity. Commonly, the effects also exhibited that the adding of fibers to usual and high act concrete upsurges the strength and advances their performance.

Keywords:
High performance concrete
Steel fibers
Polypropylene fibers
Columns
Full Text
1Introduction

High performance concrete is reached by using fibers. Conversely, using high performance concrete in construction columns in seismic parts posses extra difficulties, since it has a reduced amount of ductility associated to normal strength concrete for the reason that the rise in concrete strength decreases its ductility [1]. A compromise between these two characteristics of concrete (strength and ductility) can be achieved by adding steel fibers, since the randomly oriented fibers arrest a micro cracking mechanism and limit crack propagation, thus improving strength and ductility [2]. The addition of steel fibers to concrete not only develops the compressive strength and ductility of concrete, but also advances tensile strength, flexural strength, impact strength and toughness [3]. Presently, it has been experiential that the adding for steel fibers to great performance concrete columns effects in an rise of its internment, ductility and deformability [4,5]. Polypropylene fibers are synthetic fiber with low density, fine diameter and low modulus of elasticity. It has some special characteristics, such as high strength, ductility and durability, abundant resources, low cost, and easily physical and chemical reformations allowing to certain demands [6]. The inclusion of polypropylene fibers to concrete mix advances [7]:

  • 1

    Mix cohesion, improving pumpability over long distances.

  • 2

    Freeze–thaw resistance.

  • 3

    Resistance to explosive spalling in case of a severe fire.

  • 4

    Impact resistance.

  • 5

    Resistance to plastic shrinkage during curing.

Investigational experiments were achieved by Paultre and Eid [8]. A total of square twelve columns with 235mm cross section and height 1400mm were organized. Five concrete mixes which projected to reach the certain concrete strength with and without steel fibers. The mix was realized with silica fume; superplasticizer and steel fiber that have aspect ratio 50 with volume fraction (0.25, 0.5, 0.75, and1.0%). Three types of bars were used for the longitudinal reinforcement: bars with 11.3mm, 16.0mm and 19.5mm in diameter with indicated yield strength of 400MPa. Vahid and Togay [9] conducted the result of the adding of steel and polypropylene fibers on the manual and some durability properties of high-strength concrete (HSC). All the fiber-reinforced concretes limited 10% silica fume as a cement replacement.The effects also show that combination of steel and polypropylene fibers developed the mechanical properties of HSC measured in this study. Smarzewski and Barnat-Hunek [10] studied the effect of two extensively castoff steel fibers and polypropylene fibers on the sulphate crystallization resistance, freeze–thaw resistance and external wettability of ultra-high concert concrete (UHPC). Tests were carried out on cubes and cylinders of plain UHPC and fiber reinforced UHPC with variable contents ranging from 0.25 to 1% steel fibers and/or polypropylene fibers. Previous researches on HPC columns exhibited that the imprisonment provided by oblique steel reinforcement is less active than in normal strength concrete columns and, therefore, a high degree of confinement is required for HSC columns in order to attain similar strength and ductility improvements. In this study presents an experimental valuation of strength and ductility of normal and high concert concrete short columns limited by tie reinforcement with and wiiber reinforced UHPC with variable contents ranging from 0.25 to 1% steel fibers and/or polypropylene fibers. Previous researches on HPC columns exhibited that the imprisonment provided by oblique steel reinforcement is less active than in normal strength concrete columns and, therefore, a high degree of confinement is required for HSC columns in order to attain similar strength and ductility improvements. In this study presents an experimental valuation of strength and ductility of normal and high concert concrete short columns limited by tie reinforcement with and without steel fibers and polypropylene fibers.

2Materials

The significance of polypropylene fibers and silica fume with different arrangements on the conduct of colums concrete is measured. The materials which cast-off were including of cement [11], sand, gravel [12], steel reinforcement and conventional water is process with concrete admixtures (Superplasticizer) were used in this investigation [13].

2.1Silica fume

Silica fume is a extremely active pozzolanic material, and it is a by creation from the production of Silicon or Ferro-silicon metal. It is composed from the flue gases from electric arc furnaces. Silica fume is an awfully fine powder, with particles about 100 times smaller than an average cement grain. It is obtainable as a densified powder or in a water-slurry form. It is usually cast-off as a incomplete replacement for concrete structures that requirement high strength decrease permeability to water. ACI regulate the amount of silica fume [18]. The percentages of silica fume (5%) were used as calculation with weight of cement. The chemical oxide configuration of silica fume is assumed in Table 1, while the physical supplies are listed in Table 2. This study be contingent on to the requests of ASTM C1240-05 [14] conditions.

Table 1.

Chemical composition for silica fume.*

Oxides  Content (%)  ASTM C1240-05limitations 
SiO2  90.51  ≥85 
Al2O3  0.60  – 
Fe2O3  2.32  – 
Na20.15  – 
CaO  0.58  – 
MgO  0.3  – 
TiO2  0.01  – 
K21.26  – 
P2O5  0.11  – 
SO3  0.36  ≤4 
L.O.I  3.82  ≤6 
*

Test was carried out by testing laboratory in the College of Engineering, Kufa University.

Table 2.

Physical requirements and pozzolanic activity index for condensed silica fume(SF).*

Physical properties  SF  ASTM C1240-05 limits 
Specific surface area, min, (m2/g)  20  ≥15 
Strenght activity index with Portland cement at 7 days, min percent of control.  122  ≥105 
Percent retained on 45μm (No. 325), max, %  ≤10 
*

Tests were carried out by testing laboratory in the College of Engineering. University of Kufa.

2.2Fibers

Two types of fibers were used in this investigation.

2.2.1Steel fibers

Hooked end steel fibers which are known commercially as Dramix-Type ZC, was used in this work. These fibers were 50mm long and 0.5mm diameter (aspect ratio, l/d=100), as shown in Fig. 1. Another form of hooked steel fibers which are known as Sika Fiber SH 60/30, also used throughout the experimental program as shown in Fig. 2.

Fig. 1.

Dramix ZC 50/50 end hooked steel fibers.

(0.02MB).
Fig. 2.

Sika fiber SH 60/30 end hooked steel fibers.

(0.02MB).
2.2.2Polypropylene fibers

High performance monofilament polypropylene fibers were used in this investigation, as shown in Fig. 3. Table 3 indicates the typical properties of the used polypropylene fibers [15].

Fig. 3.

Polypropylene fibers used in this investigation.

(0.19MB).
Table 3.

Properties of the used polypropylene fibers.*

Chemical base  100% polypropylene Fibers 
Specific gravity  0.91 
Fiber length  12mm 
Fiber diameter  18μm 
Aspect ratio  667 
Water absorption  Nil 
Melting point  160°C 
Ignition point  365°C 
Acid resistance  High 
Alkali resistance  100% 
Tensile strength  (300–400) MPa 
Chloride content  Nil 
Young's modulus  (3500–3900) MPa 
Surface area  250m2/kg 
*

According to manufacturer.

2.3Reinforcing steel bars

The dimensions and strength characteristics of the steel reinforcing bars are summarized in Table 4.

Table 4.

properties of steel bars.*

Nominal bar diameter (mm)  Bar area (mm2Modulus of elasticity (GPa)  Yield stress (MPa)  Strain at yield stress (mm/mm)  Ultimate stress (MPa)  Strain at ultimate stress (MPa)  Elongatio (%) 
50.27  202  545  0.0027  660  0.18  15.5 
12  113.1  201  503  0.00252  615  0.13  14.5 

*Ø8mm manufactured by Turkish company.

*Ø12 manufactured by Ukraine company.

*Tests were carried out by testing laboratory in the College of Engineering. University of Kufa.

2.4Reinforcing steel bars for columns

conferring to the suitable ACI 318M-11 [16]. The diameters of the longitudinal reinforcing steel bars were used (12mm) one at each corner. Deformed steel bars with (8mm) diameter were also used as stirrups. Details of columns reinforcement are illustrated in Fig. 4.

Fig. 4.

Details of columns reinforcement.

*All dimension in mm.

(0.21MB).
3Control specimens

The details of the control specimens were as following:

  • 1

    Cubes of 100mm and cylinder 150×300mm for compressive strength test of concrete (f’c) were used according to BS 1881: part 116 and ASTM C39-03 [17].

  • 2

    Flexural strength test (fr) (modulus of rupture) is approved available through with (100×100×500mm) prisms, loaded at 450mm span with two points loading hydraulic machine of 2000kN capacity concrete. The trial is conceded out conferring to ASTM C78-02 [18].

  • 3

    Splitting tensile strength test(ft) is performed on a (150×300) mm concrete cylinder according to the ASTM C496-04 [19].

  • 4

    150×300mm concrete cylinders are casted for amount of static modulus of elasticity (Ec) conferring to ASTM C469-02 [20] (Table 5).

    Table 5.

    Details of the column specimens.

    Test series  Column symbol  Compressive strength of concrete (MPa)  Diameter of longitudinal reinforcement (mm) (percent ratio of longitudinal reinforcement%)  Spacing between lateral reinforcement (mm)  Type of fiber and aspect ratio  Volume fraction of fiber Vf (%)  No. of columns speimens 
    R1  About of 75  Ø 12 (4.52%)  100  Steel fibers with aspect ratio 100
      R2        0.5 
      R3        0.75 
    R4      100  Polypropylene fibers with aspect ratio 6670.5 
      R5      50  0.5 

4Testing of hardened concrete4.1Testing of concrete column specimens

Testing of concrete column specimens, as shown in Fig. 5.

Fig. 5.

Instrumentation and test setup.

(0.17MB).
5Experimental results of concrete5.1Results of mechanical properties of hardened tests

The performance of the columns be governed by largely on the properties of the basic elements, consequently it is required to training the properties of the concrete mix cast-off in industrial the column cases. Control specimens contain five cubes (100) mm, three (150×300) mm cylinders, three (100×200) mm cylinders and two (100×100×500)mm prisms for each column specimen. These specimens were prepared and tested at the same age of column specimens, all the results shown in Table 6.

Table 6.

Results of mechanical properties of hardened tests.

Mix no.  Mix proportions  w/c ratio  Type of fibers  Vf (%)  Aspect ratio of fibers  f’c MPa  Ft MPa  Fr MPa  Ec GPa 
NC  1:1.19:1.8 by weight, 2L/100kg HRWRA, silica fume 5% as addition by weight of cement0.295  –  –  –  60.33  6.43  8.91  35.54 
0.5SF100-NC  0.295  Steel fiber  0.5  100  74.53  7.87  11.08  43.79 
0.75SF100-NC  0.295  Steel fiber  0.75  100  79.37  8.93  14.84  44.83 
0.5PP100- NC  0.295  PPF  0.5  667  78.87  5.25  9.07  44.06 

PPF: polypropylene fiber with aspect ratio 667 (length 12mm and 18μm).

Vf :Volume fraction of fibers.

5.2Load-deflection results

From the load deflection curves of tested columns, it can be observed that the load versus mid-speciemens deflection response can be divided into three stages of behavior. In the first phase, a lined performance of the load deflection reaction. The first crack load start to appear, below this boundary, the materials perform elastically and the cracks creating in the tensile areas of the samples cross section are still steady. Later the cracks spread and their width upsurges with increasing load. Together the reinforcement and concrete in compression zone are still elastic. In the second stage, a nonlinear conduct of the load deflection is observed. This stage covers the region beyond the proportional limit. At this stage, the increase in the load carrying capacity beyond the proportional limit is due to the increase in the tensile stresses in steel longitudinal bars accompanied with a continuous shift in the position of the neutral axis towards the compression zone. Finally in third stage, as the applied load reaches near its ultimate value, the rate of increase in deflection is substantially exceeding the rate of increase in the value of the applied loads differents speciemens obtained the differents results for load-deflection results shown in Fig. 6.

Fig. 6.

Load-deflection relationship for concrete mixes with different fibers.

(0.08MB).
5.3Maximum strength capacity of column specimens

The influence of the dissimilar variables of the effects can be conferred as shown in Table 7.

Table 7.

Maximum strength capacity fPmax for tested column specimens.

Column symbol  Type of concrete  Type of fibers  Longitudinal reinforcement ratio  Volumetric ratio of tie  Volume fraction of Fibers  Aspect ratio of fibers  Maximum strength capacity of columns 
      ρl (%)  ρs (%)  Vf (%)  L/d  fP max(MPa) 
R1    –  4.52  2.79  –  –  48.1 
R2    Steel fibers4.52  2.79  0.5  100  56.0 
R3    4.52  2.79  0.75  100  57.5 
R4    Polypropylene fiber4.52  2.79  0.5  667  63.0 
R5    4.52  2.79  0.5  667  75.0 
6Finite element results

Finite element method is castoff to analysis slabs, the ABAQUS program affords options to describe unlike kinds of material comportment, eight – node isoparametic brick elements to signify concrete, four – node link elements for reinforcing steel [16] (Fig. 7).

Fig. 7.

Modeling of strengthened With CFRP sheets.

(0.11MB).
6.1Spaitial displacement for speciemens

Figs. 8–12 expression that the numerical load versus central column deflection for these speciemens on direction-Y and investigational records are in a useful arrangement.

Fig. 8.

Spaitial displacement for specimens R1.

(0.19MB).
Fig. 9.

Spaitial displacement for specimens R2.

(0.19MB).
Fig. 10.

Spaitial displacement for specimens R3.

(0.18MB).
Fig. 11.

Spaitial displacement for specimens R4.

(0.22MB).
Fig. 12.

Spaitial displacement for specimens R5.

(0.22MB).
6.2Concrete strain distribution

Figs. 13 and 14 expression the numerical Concrete Plastic-Strain distribution of columns. On or after this figure it can be observed that the maximum strain happened lengthways the load path where the tending crack has been happened. It also detected that the maximum rate of strain followed at position just under the mid length of load path and it is the equivalent position where the maximum crack width verified in the investigational trial.

Fig. 13.

Analytical variation of Concrete Plastic-Strain in specimens R1.

(0.22MB).
Fig. 14.

Analytical variation of Concrete Plastic-Strain in specimens R2.

(0.21MB).
7Conclusions based on experimental work results

  • 1

    Using silica fume as an addition by weight of cement increases the compressive strength of concrete. The dosage of silica fume is 5% as an addition by weight of cement with HRWRA dosage 2L/100kg of cement. This dosage of silica fume improves the compressive strength of concrete by about 25% relative to concrete mix without silica fume.

  • 2

    The addition of fibers to both NSC and HPC causes a reduction in the workability of concrete mix. The reduction in workability increases as the fiber volume fraction and aspect ratio increase. The percentage of reduction in workability is about 38% for concrete mix containing steel fibers with volume fraction 0.75% and aspect ratio 100.

  • 3

    The addition of steel fibers causes a slight increase in the compressive strength of HPC as the fiber volume fraction increases, while the compressive strength decreases as the fiber aspect ratio increases. Both splitting tensile and flexural strengths show a significant increase as the fiber volume fraction and aspect ratio increase. The percentage increase in compressive, splitting tensile and flexural strengths for HPC with fiber volume fraction 0.75% and aspect ratio100 at age 60 days is about 9%, 75%, 64%, respectively relative to non fibrous HPC.

  • 4

    The modulus of elasticity slightly increases with the increase of fiber volume fraction, while there is a slight decrease by the upsurge in fiber aspect ratio. The proportion rise for HPC comprising steel fibers with aspect ratio 100 was about 1% and 3.1% for fiber volume fractions 0.5% and 0.75%, respectively, while for fiber volume fraction 0.75%, the percentage increase was about4.6% and 3.1% for fiber aspect ratios 60 and 100, respectively relative to HPC without fibers.

  • 5

    The toughness indices of all fiber reinforced concrete are considerably enhanced over that of non fibrous concrete.

  • 6

    The volumetric ratio of longitudinal and transverse reinforcement (ties) slightly affects the peak strength of columns.

  • 7

    At the equivalent useful load, non fibrous and fibrous columns have minor deformability comparative to non fibrous and fibrous columns, this incomes that greater strength concrete columns involve extra imprisonment than ordinary strength concrete columns.

  • 8

    The deformability of steel fiber high enactment concrete columns after concrete cracking rises as the fibers aspect ratio is improved.

Conflict of interest

The authors declare no conflicts of interest.

Ethical statement

Authors state that the research was conducted according to ethical standards.

Funding

None.

Acknowledgments

The author expresses greetings to thank All the staff of Structural materials laboratory and the library staff for their assistance in preparing the work tests were conducted in the construction materials laboratory of the Najaf technical institute, Al-furat Al-awsat technical University, to accomplish this research.

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Copyright © 2019. The Authors
Journal of Materials Research and Technology

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